The basal lamina extracellular matrix that surrounds myofibers has a profound influence on developing and adult neurons and muscle cells, and many of this effects can be attributed to the glycoprotein laminin. The long term goal of this research is to understand how neurons and muscle cells interact with and respond to laminin. Several cell surface laminin receptors have been described bur their specific functions are unclear. The focus of this grant is to determine the function of aspartactin, a newly discovered muscle surface laminin binding protein whose role in development is unknown. Proposed experiments will make use of new and existing antibodies and cDNA clones to characterize the spatial and temporal pattern of aspartactin gene expression, particularly with regard to regulation during myogenic differentiation in skeletal muscle. In addition, a detailed investigation of the interaction between aspartactin with laminin will be completed. Next, the importance of aspartactin in myoblast response to laminin and in myotube assembly of laminin in the basal lamina will be evaluated. The perturbing effects of purified aspartactin, as well as antibodies against aspartactin that block laminin binding, will be examined in a battery of in vitro assays. Function will also be assessed genetically by obtaining mutant cell lines with increased or decreased aspartactin expression. Mutants will be obtained via sense and antisense expression of cloned chick and rat aspartactin cDNAs and by selection using anti-aspartactin antibodies and complement. A phenotype related to altered aspartactin expression will be sought. Knowledge of muscle interactions with the basal laminal will contribute greatly to an understanding of normal development processes that are disrupted during disease. the proposed research should be pertinent to understanding the basic biology that is in disarray in debilitating neuromuscular degenerative diseases. This work may also shed light on how tumor cells pass through basal lamina boundaries during metastasis.